Manufacturing machinery and other types of equipment oftentimes present one or more hazards to their operators or other adjacent personnel. Such machinery can be designed to minimize the hazards, and protective guards may be available to further mitigate the danger in some instances. However, it is often not possible to completely eliminate machinery hazards through protective guarding alone.
As an example, work piece loading and unloading operations routinely require machine operators to access or otherwise enter hazardous machine areas. While it is desirable for a worker to have access to a machine during such loading and unloading operations, it is frequently necessary to restrict such access during working phases of the machine. Light curtains are commonly used in this type of machine guarding application, and find broad use in a variety of other applications as well.
A typical light curtain comprises a receiver unit and a transmitter unit, along with supporting electronics and one or more machine control outputs. Light beams are transmitted across a hazardous area in or around a guarded machine from the transmitter unit to the receiver unit. When one or more light beams are blocked, such as by a human entering the hazardous area, the receiver unit detects the blockage and provides a signal to the supporting electronics which de-energizes the machine control outputs or otherwise removes power from the guarded machine.
As a type of optical presence sensing device, light curtains are available in a wide variety of types and configurations. Examples range from single beam models with simple on/off machine control, to sophisticated systems with hundreds of light beams and the ability to provide selective machine guarding in accordance with the loading, processing, and unloading cycles of the guarded machine. Other variations include reflective based systems, where reflectors are used to redirect transmitted light beams back to receiving units, which may be co-located with transmitting units, or to other reflecting units to extend the light beam coverage.
Indeed, extending the light beam coverage to conform to the sometimes-complex shapes of hazardous areas poses particular challenges. For example, multi-beam light curtains typically include a transmitter segment that comprises a linear array of spaced apart light emitters, with the receiver segment comprising a corresponding linear array of similarly spaced light receivers. Aligning the transmitter with the receiver forms a single plane of protection, which is suggested by the term xe2x80x9clight curtain.xe2x80x9d However, machines commonly have potentially hazardous areas both above and below a work piece loading area.
One approach to adapting rigid light curtains to such applications uses multi-segmented light curtains that may be made to conform to the dimensions of the hazardous area. With this approach, the receiver and transmitter units comprise a like number of individual segments that are pieced or coupled together. Generally, the intersection between individual segments may be fixed at one or more angles, thereby allowing the segmented transmitter and receiver units to follow more complex contours and angles.
Oftentimes, receiver and transmitter light curtain segments use the same or at least very similar segment housings, connectors, and cables for economic and manufacturing reasons. However, the similarities cause a common field installation error of mistakenly interconnecting receiver type light curtain segments with transmitter type light curtain segments. At the least, this type of misconnection causes frustration and delay, and may also result in damage to misconnected segments. Thus, a segment connection system that uses the same parts or pieces for both receiver and transmitter segments and yet prevents segment misconnection is needed.
The present invention comprises a method and apparatus for connecting light curtain segments together to form multi-segmented light curtains, while preventing misconnection between receiver type segments and transmitter type segments. A connector comprises first and second halves or mating sections, with each connector half mounting to a respective light curtain segment and allowing interconnection of the respective segments. The same connector is used to join both transmitter and receiver light curtain segments, but is configured in a first relative orientation for use with transmitter type segments, and is configured in a second relative orientation for use with receiver type segments. The differing configurations of the connector prevent misconnection of transmitter segments with receiver segments.
In an exemplary embodiment, the mating sections comprise a coupler assembly and a mating receptacle. A coupler portion of the coupler assembly is preferably made as a detachable plate or tongue that mounts to one end of a light curtain segment. The coupler has one or more distinct features, such as protruding tabs. The mating receptacle, which mounts to an end of another segment, comprises receiving features, such as tab seats (e.g., cavities) that accommodate the protruding tabs of the coupler. By mounting the coupler to a segment in a first orientation, its protruding tabs occupy first positions relative to the mating receptacle. Reverse mounting the coupler reverses its tabs to second positions relative to the mating receptacle. By including first and second sets of tab seats as receiving features in the mating receptacle, it operates to receive the coupler in either the first or second orientations.
Preferably each set of tab seats include keying holes positioned within the cavities defining the tab seats. A keying pin or other type of blocking post or stud may be positioned in any of these keying holes. If keying pins are fixed within the second set of tab seats, couplers in the second configuration cannot be mated with the receptacle. Conversely, positioning keying pins within the first set of tab seats prevents couplers in the first orientation from mating with the receptacle. In this manner, the same receptacle may be used for both receiver type and transmitter type light curtain segments and selectively keyed as needed. Preferably, the keying holes are threaded such that the keying pins may be conveniently installed or removed as needed.
The coupler generally includes one or more mounting holes, with corresponding mounting holes in the receptacle. Screws or other type of fastener may thus be used in conjunction with these mounting holes to securely connect the coupler assembly to the receptacle, thus securely joining the light curtain segments together. In addition to providing for secure physical connection between segments, the coupler assembly and receptacle preferably include complementary signal connectors that interconnect the various signals running between the interconnected segments.
In other embodiments, the first and second mating sections comprise mating blocks having complementary mating features. By reversing the orientation of one or both of these mating sections relative to the light segments on which they are mounted, depending on whether the segments are receiver types or transmitter types, misconnection between dissimilar segment types is prevented. One or both of the mating sections may be rotatably mounted on its respective segment, thereby allowing articulation of joined segments.